The immediate objective of this research is to complete the refinement of the model for hen egg white lysozyme in the triclinic crystal form at 2Angstrom resolution and subsequently to extend the study to much higher resolution significant reflection intensity having been observed to d spacings of at least 1Angstrom. The methods used to refine the model will be restrained least squares, ultimately to be combined with energy minimization. An important objective of the lysozyme refinement is a model sufficiently precise to reveal differences of structure that arise from differences of packing of the molecules in the tetragonal and triclinic crystal forms and to compare the B parameters of the two models that indicate the molecular flexibility related to the internal structure of the molecule. One part of the study will test the efficiencies of different refinement programs and the dependence of the resulting molecular parameters on the values used for restraints and weighting factors used in the programs. A long-term objective is to determine the kinds of errors that may remain in models refined against data sets of various resolutions and to assess the R index as a measure of model reliability.